An Etymological Dictionary of Astronomy and Astrophysics

فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory



<< < act dwa H I Lym ret ult > >>

Number of Results: 105 Search : Galaxy
retired galaxy
  کهکشان ِ بازنشسته   
kahkešân-e bâznešasté

Fr.: galaxie retraitée   

An old galaxy with faint emission lines whose ratios are similar to those of → LINERs, i.e. galaxies with low-ionization nuclear emission-line regions. All galaxies after consuming their → molecular clouds, where stars are formed, follow a "passive" evolution during which their → stellar populations simply get older and older. The old stellar populations contain hot post-→ AGB stars and → white dwarfs which are able to ionize the surrounding gas and produce spectra identical to those of LINERS.

Retired in the sense "withdrawn from or no longer occupied with one's business or profession," p.p. of retire, from M.Fr. retirer "to withdraw (something)," from → re- "back" + O.Fr. tirer "to draw;" → galaxy. The concept of retired galaxies was first proposed by G. Stasińska et al. (2008, MNRAS 391, L29) to name the final stages of galaxies that cease their star forming activity. The word "retired" is also to be taken by opposition to "active" in the sense of "containing an accreting black hole" (like Seyfert galaxies), since liners are often thought to be a scaled down version of Seyfert nuclei.

Bâznešasté "retired," literally "seated back, seated away," from bâz-re- + nešasté "seated," p.p. of nešastan "to sit;" Mid.Pers. nišastan "to sit;" O.Pers. nišādayam [1 sg.impf.caus.act.] "to sit down, to establish," hadiš- "abode;" Av. nišasiiā [1 sg.subj.acr.] "I shall sit down," from nihad- "to sit down," from ni- "down, in, into," → ni-, + had- "to sit;" PIE base *sed- "to sit;" cf. Skt. sad- "to sit," sidati "sits;" Gk. hezomai "to sit," hedra "seat, chair;" L. sedere "to sit;" O.Ir. suide "seat, sitting;" Welsh sedd "seat;" Lith. sedmi "to sit;" Rus. sad "garden;" Goth. sitan, Ger. sitzen; E. sit.

ring galaxy
  کهکشان ِ حلقه‌ای   
kahkešân-e halqeyi

Fr.: galaxie en anneau   

A galaxy with a ring-like appearance around the central luminous center. The ring consists of massive, relatively young bright stars. It is believed that ring galaxies result from the head-on collision of two different galaxies.

ring; → galaxy.

Sagittarius Dwarf Elliptical Galaxy
  کهکشان ِ کوتوله‌ی ِ بیضی‌گون ِ نیم‌اسب   
kahkešân-e kutule-ye beyzigun-e nimasb

Fr.: galaxie naine elliptique du Sagittaire   


Sagittarius; → dwarf; → elliptical; → galaxy.

Sagittarius Dwarf Irregular Galaxy
  کهکشان ِ کوتوله‌ی ِ بی‌سامان ِ نیم‌اسب   
kahkešân-e kutule-ye bisâmân-e Nimasb

Fr.: galaxie naine irrégulière du Sagittaire   


Sagittarius; → dwarf; → irregular; → galaxy.

satellite galaxy
  کهکشان ِ بنده‌وار   
kahkešân-e bandevâr

Fr.: galaxie satellite   


satellite; → galaxy.

Sculptor Dwarf Elliptical Galaxy
  کهکشان ِ کوتوله‌ی ِ بیضی‌گون ِ پیکرتراش   
kahkešân-e kutule-ye beyzigun-e Peykartarâš

Fr.: galaxie naine elliptique du Sculpteur   

A → dwarf elliptical galaxy that is a satellite of our → Milky Way. It lies about 285,000 → light-years away in the constellation → Sculptor, and has an → absolute magnitude of -11.28 and a mass of about 3 million → solar masses. The Sculptor Dwarf is a → metal-deficient galaxy containing only 4 percent of the oxygen and carbon elements in our own Galaxy.

Sculptor; → dwarf; → elliptical; → galaxy.

Seyfert galaxy
  کهکشان ِ سیفرت   
kahkešân-e Seyfert

Fr.: galaxie de Seyfert   

A member of an important class of → active galaxies which are characterized by the presence of an intensely bright nucleus in the optical wavelengths (109-1012Lsun) displaying emission spectral lines. The presence of these emission features, which are not seen in the spectra of normal galaxies, indicates a very high degree of ionization. Moreover, the nucleus radiates → non-thermal  → continuum emission extending over the whole electromagnetic spectrum. It is thought that a → massive black hole in the nucleus of a galaxy accretes gas (→ accretion) from its surrounding environment to power Seyfert galaxies. These galaxies are divided into two types according to the width of their spectral lines. Type 1 Seyfert (Sy 1) galaxies have very broad emission lines (103- 104 km s-1), while Type 2 Seyferts (Sy 2) show relatively narrow lines (several hundred km s-1). These spectral differences may be the result of viewing the nucleus from different angles. A Type 2 Seyfert galaxy may be a mostly edge-on view of matter spiraling in toward the supermassive black hole, whereas a Type 1 Seyfert provides a more pole-on view, allowing us to see the more turbulent region around the black hole.

Named after Carl Keenan Seyfert (1911-1960), the American astronomer who first identified this type of galaxies in 1943; → galaxy.

shell galaxy
  کهکشان ِ پوسته‌دار   
kahkešân-e pustedâr

Fr.: galaxie en coquille   

An elliptical galaxy that is surrounded by thin shells of stars which are thought to have been ejected during a galaxy merger. Shell galaxies are different from ring galaxies in that the shells are much further away from the galaxy's centre and much fainter than the rings. Spectroscopy of the stars in the shell show that they are old whereas the stars in a ring galaxy are young.

shell; → galaxy.

Sombrero galaxy
  کهکشان ِ سومبررو   
kahkešân-e Sombrero

Fr.: galaxie Sombrero   

A → spiral galaxy in the constellation → Virgo. It was the first galaxy whose rotation was detected. Also named M104 and NGC 4594.

Sp. sombrero "broad-brimmed hat," originally "umbrella or parasol," from sombra "shade," from L.L. subumbrare, from → sub- "under" + umbra "shade, shadow;" → galaxy.

Kahkešân, → galaxy; sombrero, Sp., as above.

Spindle Galaxy
  کهکشان ِ دوک   
kahkešân-e duk

Fr.: galaxie du Fuseau   

Same as → NGC 5866.

spindle; → galaxy.

spiral galaxy
  کهکشان ِ مارپیچ   
kahkešân-e mârpic

Fr.: galaxie spirale   

A galaxy with a prominent nuclear → bulge and luminous → spiral arms of gas, dust, and young stars that wind out from the nucleus. Masses span the range from 1010 to 1012solar masses.

spiral; → galaxy.

star-forming galaxy
  کهکشان ِ دیسنده‌ی ِ ستاره   
kahkešân-e disnade-ye setâré

Fr.: galaxie de formation d'étoiles   

A galaxy that is located on the → galaxy main sequence in the plane relating → star formation rates to total stellar masses.

star; → formation; → galaxy.

starburst galaxy
  کهکشان ِ ستاره-بلک   
kahkešân-e setâre-belk

Fr.: galaxie à flambée d'étoiles   


starburst; → galaxy.

strong arm spiral galaxy
  کهکشان ِ مارپیچ با بازوی ِ سترگ   
kahkešân-e mârpic bâ bâzu-ye setorg

Fr.: galaxie spirale à forts bras   

A galaxy with prominent stellar → spiral arms and little star formation between stellar arms, such as M51.

strong; → arm; → spiral; → galaxy.

submillimeter galaxy (SMG)
  کهکشان ِ زیر-میلیمتری   
kahkešân-e zir-milimetri

Fr.: galaxie sub-millimétrique   

A member of an extremely luminous population of → high-redshift galaxies which are detected in → submillimeter waves (→ flux density at 850 μm ≥ 3 - 5 mJy). SMGs are powered primarily by star formation rather than an → active galactic nucleus (AGN). Because of their high → dust content, these galaxies emit almost all of their luminosity in the infrared, with a → bolometric luminosity ranging from 1012-1013 → solar luminosities. As such, SMGs resemble → ultraluminous infrared galaxies (ULIRGs), which are almost exclusively → merging galaxies. Indeed, many observations support a → merger origin for SMGs (see, e.g. C.C. Hayward et al. 2011 and references therein, astro-ph/1101.0002).

submillimeter; → galaxy.

superthin galaxy
  کهکشان ِ اَبَرنازک   
kahkešân-e abarnâzok

Fr.: galaxie supermince   

A galaxy that appears as an extraordinary thin and long figure on the sky because of its → edge-on orientation, highly flattened stellar → disk, and absence of a → bulge component. Superthin galaxies are → gas-rich and have optically diffuse disks with little internal absorption, as well as low emission-line intensity ratios and slowly rising → rotation curves. They seem to be among the least evolved disk galaxies in the local Universe, having undergone only minimal dynamical heating, → star formation, and → angular momentum transport. Examples are: UGC 7321, UGC 3697, UGC 9242.

super-; → thin; → galaxy.

superwind galaxy
  کهکشان ِ اَبَر-باد   
kahkešân-e abar-bâd

Fr.: galaxie à super-vent   

A galaxy with → superwind characteristics. M 82 and NGC 4666 are among superwind galaxy candidates.

superwind; → galaxy.

tidal dwarf galaxy
  کهکشان ِ کوتوله‌ی ِ کشندی   
kahkešân-e kutule-ye kešandi

Fr.: naine de marée   


tidal; → dwarf; → galaxy.

Triangulum galaxy (M33)
  کهکشان ِ سه‌بر   
kahkešân-e sebar (#)

Fr.: galaxie du Triangle   

One of the prominent members of the → Local Group situated in the constellation → Triangulum. Also know as NGC 598. M33 is a type Sc → spiral galaxy seen nearly → face-on. It lies 2.8 million → light-years away and its diameter is 52,000 light-years. M33 is thought to be a satellite of the → Andromeda Galaxy.

Triangulum; → galaxy.

ultracompact dwarf galaxy (UCD)
  کهکشان ِ کوتوله‌ی ِ اولتر-همپک   
kahkešân-e kutule-ye ultar-hampak

Fr.: galaxie naine ultracompacte   

A type of very bright compact → stellar system (-14 ≤ MV≥ -12) that is intermediate between → globular clusters (GCs) and → compact elliptical galaxies (cEs). With masses of M > 2 × 106 Msun and radii > 10 → parsecs (pc), UCDs are among the densest stellar systems in the Universe. Nevertheless, the nature and origin of these objects is still widely debated. Early interpretations suggested that UCDs could be the most massive GCs or possibly the → tidally stripped remnants of → dwarf galaxies. However, there is evidence that both formation mechanisms could contribute to the UCD population. → Supermassive black holes (SMBHs) have been confirmed in most UCDs with masses M > 107 Msun. The most massive UCD discovered to date, M59-UCD3 (M* ~ 2 × 108 Msun, radius ~ 25 pc), hosts a SMBH (Ahn et al., 2018, arxiv/1804.02399, and references therein).

ultracompact; → dwarf; → galaxy.
